The present invention relates to tricycles, and more particularly to recumbent tricycles having steerable twin rear wheels.
Of passenger-propelled vehicles, tricycles provide a vehicle which is more stable than a bicycle and has a turning radius which is usually smaller than that of a four-wheeled vehicle. Furthermore, unlike bicycles, a three-wheeled passenger-powered vehicle may include a relatively comfortable seat which provides support for the back of the operator and allows the operator to ride in a recumbent position. Such tricycles are known as recumbent tricycles.
One type of recumbent tricycle consists of a frame, a single pedal-driven rear wheel, and twin steerable front wheels. One disadvantage of this design is that the single rear wheel affords only a single point of support of the rear of the vehicle, which typically bears the bulk of the weight of the operator, and therefore such vehicles often become unstable during sharp turns. Another disadvantage is that the drive mechanism, typically a pedal-driven chain and sprocket drive, requires that a sprocket chain pass beneath the operator's seat to the rear wheel, necessitating a higher seat and hence a higher center of gravity, which reduces stability.
A different type of recumbent tricycle includes a frame mounting a single front wheel and steerable twin rear wheels. The advantage of this design is that the twin wheels each bear a portion of the higher rear load and also provide two spaced apart points of support to the rear of the vehicle which increases the stability of the vehicle when turning.
For example, in the Mulcahy U.S. Pat. No. 4,359,231, a tricycle is disclosed having a single front wheel and two steerable rear wheels. The rear wheels are rotatably mounted to an axle which is pivotally mounted to the frame of the tricycle at a central rearward portion thereof. A pair of steering handles are rigidly mounted to the frame on either side of the passenger seat, and the passenger turns the vehicle by grasping the handles and leaning, thereby causing the rear axle to pivot and point the rear wheels away from a forward facing direction.
A disadvantage with that type of design is that the tricycle lacks a positive steering mechanism which turns either the front or rear wheels in a predictable or gradual manner to effect a predetermined rate of turning. Another disadvantage with this type of steering mechanism is that it would be difficult for the operator to pedal such a vehicle and at the same time maintain the rear wheels in a turning configuration by leaning to the side. Furthermore, it would be difficult for the operator to adjust his weight sufficiently rapidly to vary the direction of the tricycle from a sharp turn in one direction to a sharp turn in the opposite direction. Indeed, such rapid shiftings of the body weight of the operator might cause the tricycle of that design to lose stability.
Accordingly, there is a need for a recumbent tricycle which can support an operator comfortably and have twin steerable rear wheels which can be turned gradually and predictably by the operator so that sharp turns can be effected without significantly affecting the stability of the vehicle. There is also a need for a recumbent tricycle in which the front wheel is powered, thereby obviating the need to raise the operator seat to provide clearance for a rear wheel drive train to pass thereunder. It is also desirable to fabricate a tricycle having the aforementioned characteristics such that it includes a relatively lightweight frame and relatively easily constructed steering and propulsion components.